1. Field of the Invention
This invention pertains to a construction product in sheet form for roof decks and related applications, to a method of joining the sheets, and to roof decks composed of the sheets joined according to the invention.
2. Description of the Prior Art
Multilayered construction material in sheet form, having a mineral-based inner layer and a foamed plastic intermediate layer, for use in roof decks and related applications are known in the industry. The U.S. Pat. No. 3,889,836 to Payne shows such a building component comprising a glass fiber-reinforced gypsum inner layer, a foamed polyisocyanurate or polyurethane intermediate layer, and an outer layer of water-resistant sheet of sanded bituminized roofing felt. Upon application or assembly, the sheetsor panels disclosed in Payne are joined and then the joined panels are covered with two or more layers of the sanded bituminized roofing felt, thus giving rise to the term "built-up roofing" used to describe this type of construction. Built-up roofing is currently a standard technique for waterproofing in the industry.
Current products for the roof deck market do not solve two major, interrelated problems that accompany the use of the "built-up roofing" technique, namely (1) the necessity to employ on-site finishing of the panels or assembled roof deck, and (2) the reliance on hot-asphalt-type finishing materials.
On-site finishing of the exposed surface of the exterior layer of the panels is labor intensive, and, with skyrocketing wage rates, labor can be a significant portion of the total cost of built-up roofing. In addition, a quality built-uproofing assembly requires a certain amount of craftsmanship to insure leak-free operation for reasonable period of time. The National Bureau of Standards, in its publication entitled "The Effect of Moisture on the Heat Transfer Performance of Insulated Flat-Roof Construction," Building Science Series No. 37, listed "a steadily worsening quality of workmanship" as one of the primary reasons for a deterioration in the average quality of built-up-roofing in the past few years. This same publication suggests that poor workmanship, along with certain material quality and construction factors, causes most built-up roofs to leak within two years, certainly an unacceptably short period of time. The use of pre-finished roof deck panels or those which would require a minimum of high-cost labor for installation is thus a highly desirable and much sought after goal in the construction industry and is an object of the present invention.
Although a steadily worsening in the quality of asphalt and roofing felt was another factor mentioned in the Bureau of Standards publication, the use of asphalt has additional drawbacks. Hot asphalt is difficult to apply in extreme temperature conditions, and increasing pollution control and health safety requirements are making it more difficult and expensive to work with. Also, fire underwriters would prefer to eliminate asphalt entirely from roof decks but are reluctant to press for revised building codes until equal or lower cost alternatives are available.
Alternative sheet materials presently available in the market are either too costly or lack the capacity to accommodate significant expansion and shrinkage of the sheets in response to temperature changes while retaining water-impermeability. This latter factor becomes critical in structures such as shown in Payne, or applicants' own invention, wherein insulation is positioned directly beneath the sealing layers. This pre-formed insulation facilitates unit body construction but causes greater temperature extremes at the sealing surface, with consequently more severe thermal expansion and contraction of that surface taking place. A construction product utilizing materials other than layered asphalt felt or any asphaltic sealer but having the capacity to accommodate significant expansion and contraction would be expected to make a significant contribution to the building industry and is another object of the present invention.